WASHINGTON (AP) _ Stung by yet another embarrassing sex-related incident, the Navy is ordering everyone in the service to pause for 24 hours of ``preventive maintenance'' against future breakdowns in discipline.

``It's time for the Navy to take a day and stand down and take a hard look at ourselves,'' Adm. Mike Boorda, the chief of naval operations, said Thursday. The day of introspection will be observed on a rotating basis by units worldwide, he said.

The purpose will be to think of ways to avoid discipline problems before they happen.

Boorda's announcement came after The Washington Post reported Thursday that a drunk Navy cook sexually assaulted a female sailor aboard a commercial jet and that the 20 or so other sailors on the flight chose not to intervene.

The Post said the alleged offender was a 49-year-old chief petty officer and the victim was a 23-year-old 3rd class petty officer. The Post said none of the sailors on the flight intervened other than to ask the woman if she was all right.

In San Diego, Lt. Cmdr. Bruce Cole, a Navy spokesman, said it was not true that no one intervened. ``Action was taken on her behalf to stop the incident,'' Cole said, but he would not say what action was taken or by whom.

Boorda said he could not comment on the sexual assault case because it is under investigation by the Naval Criminal Investigative Service. But in summoning several reporters to his headquarters office in the Pentagon, the admiral made no secret of the fact that the reported incident prompted him to act.

The Post report ``troubled me,'' Boorda said, but added that his order for a daylong ``stand down'' for the Navy worldwide was in response to a string of embarrassing episodes recently that reflected poorly on the Navy. Among these, he said, was the Naval Academy's announcement this week that it is investigating 22 midshipmen for alleged marijuana and LSD use. On Oct. 15 two midshipmen were arrested at a hotel where LSD, a hallucinogen, allegedly was found.

And there have been these other recent incidents:

_A 22-year-old Navy seaman based in Okinawa is on trial there, along with two Marines, for the rape of a 12-year-old Japanese girl. The seaman, Marcus D. Gill, admitted in court Tuesday that he raped the girl after abducting her Sept. 4.

_Navy Capt. Everett Greene, leader of a SEAL commando unit and a former head of the Navy's equal-opportunity office, was charged with having an ``unduly familiar'' relationship with a female subordinate. He was acquitted in a court-martial in Washington last month, but Navy Secretary John Dalton decided this week to recommend that his scheduled promotion to admiral be stopped.

All this comes four years after the Tailhook scandal of September 1991 in which drunken Navy and Marine Corps aviators at a convention in Las Vegas groped and sexually harassed more than two dozen female colleagues.

The last time the Navy called a service-wide ``stand down'' was in 1992 in response to Tailhook. During a ``stand down,'' normal duties are suspended to focus on a particular problem, such as a rash of accidents.

Boorda said he saw no reason to impose any new or tougher behavior standards or regulations, but wanted every sailor to think about how to stay out of trouble.

``Most of what we are talking about is common sense,'' he said.

As an example of the ``preventive maintenance'' he thinks is needed, Boorda cited the ``buddy system'' for sailors on liberty at foreign ports in which sailors go ashore with a friend so that help is available if needed.

Boorda said he saw a pattern of alcohol-related behavior problems. ``That will definitely be a focus of what we talk about'' on the service-wide day of reflection, he said.

Boorda stressed that he believes the vast majority _ ``99.99-something percent'' _ of people in the Navy do not get in trouble off ship or station. Still, he said, the percentage who do is ``too darned big and I want to make it smaller.''

Asked why the Navy continues to find itself mired in embarrassing behavioral problems, often involving alcohol use and sexual harassment or assault, even after the Tailhook episode, Boorda struggled to avoid sounding defensive.

``I don't want to make excuses for the Navy,'' he said, but added that because there are 433,000 people on active duty in the Navy, ``there are going to be a few people who don't get the word'' on what is unacceptable behavior.